The present invention relates to automotive alternators and similar electrical machines and their controls.
Most modern automobiles include a charging system which include a battery, an alternator and a regulator. In such charging systems, the alternator is mechanically coupled to the engine whereby the engine will rotate the rotor of the alternator when the engine drive shaft is rotating. When the engine is operating, the alternator is used as a generator to recharge the battery and provide electrical power to various electrical loads, e.g., headlights, of the vehicle. Alternators are typically multiphase electrical machines, typically three-phase. The electrical power generated by the alternator is dependent upon several variables, two of the more significant variables are the engine speed, the rotational speed of the alternator rotor generally varies with the engine speed, and the voltage of the field coils on the rotor of the alternator.
A regulator senses the voltage of the charging system and regulates the voltage of the field coils of the alternator rotor to maintain the voltage of the charging system at the desired level as the engine speed and electrical loads vary. The battery not only acts as an electrical power reservoir but also acts as a buffer dampening such variations.
As a higher voltage is provided to the field coils, a greater torque will be required to rotate the alternator rotor at any one speed. In other words, when the voltage of the field coils is increased to increase the output of the alternator, the alternator will drain additional horsepower from the engine.
When initially starting the engine of a typical automobile, the battery powers an electrical starter motor which turns a flywheel and thereby turns over the engine. The starter provides torque to the engine for a brief period of time until the engine starts to operate normally and no longer needs assistance. Under colder conditions, the time required to start the engine is lengthened and the starter may be required to provide torque for a longer period of time.
In such cold start conditions when the starter is activated for a relatively long period of time, the voltage of the alternator field coils may be increased to normal operating levels while the starter is still activated. In such a situation, the alternator will be unnecessarily parasitic on the starter, draining mechanical energy from the engine as the starter is providing mechanical energy to the engine and thereby extending the crank time of the starter and lengthening the time required for the engine to reach a stable idle condition. Such a prolongation of the crank time and associated delay of stable idle condition is generally undesirable.